Dehydrohalogenation of dihalopropionic acid compounds



Patented May 26, 1953 UNITED STATES PATENT OFFICE DEHYDROHALOGENATION OF DIHALOPRO PIONIC ACID COMPOUNDS William 0. Ney, Jr., Somerset Center, Mass, as-

signor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November 3, 1950, Serial No. 194,018

8 Claims.

1 This invention relates to a process for the preparation of esters, amides and nitriles of ahaloacrylic acids by dehydrohalogenation of the corresponding esters, amides and nitriles of a dihalopropionic acid in which at least one of the halogens occupies the 0.- position; and it is an object of this invention to provide an improved process for such dehydrohalogenations.

More specifically, the invention relates to the preparation of esters of a-chloroacrylic acid by dehydrochlorination of the corresponding esters of a,,3-dichloropropionic acid.

U. S. P. 2,245,547 to Pollack discloses dehydrohalogenation of dihalopropionic acid esters with sodium, potassium, calcium or magnesium hydroxides, carbonates or bicarbonates in the presence of water, perferably insufficient to form a solution of the alkaline dehydrohalogenating agent. However, this method has serious drawbacks in that the ester tends to saponify in the presence of the aforesaid alkaline reacting materials, and the process therefore requires that the alkaline dehydrohalogenating agent be added to the dihalopropionic acid ester at a rate substantially corresponding to that of the formation of the haloacrylic ester; further, that the a-halo- .acrylic ester produced be removed substantially as rapidly as it is formed from the reaction mixture, and that the amount of water present in the mixture be controlled to avoid an excess thereof.

These conditions are difiicult to maintain, and the process is therefore relatively unsuitable for com- -.mercial use.

I have discovered that the disadvantages of the aforesaid process are avoided by employing, instead of the alkaline dehydrohalogenating agents disclosed in the Pollack patent, an aqueous solution of an alkali metal monohydrogen phosphate as the dehydrohalogenation agent, especially in the presence of an alkali metal dihydrogen phosphate, whereby the aqueous reaction mixture acquires an acid reaction, e. g. a pH between 4 and I and preferably from 5 to 6, during all or almost all of the dehydrohalogenation.

One method of carrying out the process of my invention involves heating a dihalopropionic acid ester, amide or nitrile, as defined above, with an aqueous solution of an alkali metal monohydrogen phosphate (e. g. disodium hydrogen phosphate) in an amount corresponding to 1 to 3 mols per molecular equivalent of dihalopropionic acid in the dihalopropionic ester, amide or nitrile.

During the initial stages of dehydrohalogenation (e. g. when the reaction has proceeded to the extent of 5 to 10 of completion), a sufiicient 2 amount of alkali metal dihydrogen phosphate is formed to render the aqueous solution weakly acidic, and the major portion of the reaction thus takes place in an acidic rather than an alkaline dehydrohalogenating medium.

In a variation of the foregoing procedure, a minor proportion of an alkali metal dihydrogen phosphate (or a corresponding amount of phosphoric acid or another acid stronger than phosphoric acid or of comparable strength) is added to the alkali metal monohydrogen phosphate in the aqueous dehydrohalogenating reaction mixture, the amount of the dihydrogen phosphate or acid being sufiicient to reduce the pI-I to less than 7 and preferably to about 6. A mixture containing mol per cent of alkali metal mono- .hydrogen phosphate and 5 mol per cent of alkali metal dihydrogen phosphate is suitable for this purpose. The aqueous dehydrohalogenation solution thus obtained is heated with a dihalopropicnic ester, amide or nitrile, the proportions being Such that at least 1 mol of alkali metal monohydrogen phosphate is present per molecular equivalent of dihalopropionic acid of the ester, amide or nitrile employed. Preferably, an excess of alkali metal monohydrogen phosphateis included, so as to prevent an excessive decrease in pH during the reaction. For example, an excess of 10 to 200 mol per cent can be suitably employed.

, The concentration of the alkali metal monohydrogen phosphate in the aqueous solution of the reaction mixture is limited only by the solubility of the salts therein at the reaction temperature. To insure a satisfactory rate of reaction, the concentration of the alkali metal monohydrogen phosphate should not be substantially less than 10 and is preferably not less than 30 in the aqueous portion of the reaction mixture at the beginning of the reaction. Preferably, a sufficient amount of the alkali metal monohydrogen phosphate is used to maintain a concentration of at least 10% thereof in the aqueous portion of the reaction mixture until the end of the reaction.

The dehydrohalogenation is carried out by heating the reaction mixture at temperatures from about 60 to the boiling point of the mixture, e. g. to about C. At these temperatures, the reaction is ordinarily complete Within 1 to 5 hours. Higher temperatures (e. g. up to C.) can be employed by applying sufficient. pressure to maintain the mixture in the liquid phase.

The reaction is conveniently carried out by heating the dehydrohalogenation mixture under ture together with water, from which it can be separated, and subsequently purified :by further distillation. The phosphates present'in the reaction mixture are non-volatile and LCaHSGTHO eCOXltamination of the product. When :the .u-haloacrylic acid compound produced is-relati-vely-"nonvolatile, so that distillation isinconvenient, the product can be recovered from the reaction mixture by extraction with a volatile organic solvent, and recovered from the extract in knownmanner. The insolubility of the phosphates of the reaction zmi-xture inorganic solvents again. prevents contaminationofzthe products with these -reagents.

'The process is .preferably 'zapplied to 11,5- dihalopropionic acid esters, especially p-"di- ,chloropropionic :acidesters for the ;,preparati'on .of the-corresponding .a-haloacrylic acid esters. 'Iihezlowerresters are yolatile, .and can be readily recovered from :the reaction mixture eby disitillation.

Since ;the aehaloacrylic .acid :esters, amides and nitriles produced in .the process .of :the invention are susceptible to polymerization, .it ds sgenerailly desirable toincludea small amount of -a polymerization inhibitor .such :as tertiary butyl rcatechol, .hyd-roquinone, .ptphenylene -diamine, :picric acid, copper -or "copper compounds innthe :reactionmixtu-re, and to shield the mixture from -.actin-ic light, in -.orde1' :to avoid polymerization :of -the products. lit is--also of advantageto .carry out the reaction in an atmosphere of an inert :gas such as nitrogen.

'Theprocess of my inventionisil-lustrated by the following examples, wherein the parts are by weight unless --other-w-ise indicated, and parts by volume mean the volume occupied by an equ-a-lnumberof par-ts by weight of'wa-ter.

Example 1 628 parts (4 mols) of methyl a,,B-'d-iGhlU1O- propionate containing 3 parts ofpicric acid (a polymerization inhibitor) dissolved therein, were heated to-50--C.,'and added-to l575-part-s (4&4 mols) --of melted disodi-um hydrogen phosphate dodecahydr-ate-at'oo c. The mixture, preferably 1 of methyl a,;8-dichloropropionate remained as a higher boiling residue. These results correspond -toa conversion of 52% of the methyl a;p-dichloropropionate and a yield of methyl a-chloroacryl'ate amounting to 78% of theory.

Ewample 2 Asoiution of 1320 parts (9.3 mols) of anhydrous disodium hydrogen phosphate in 2000 parts of water was added to a mixture of 1295 parts (83 mols) of methyl -a,,8-dichloropro- 'zdichloropropionate were recovered.

pionate containing 6.5 parts of picric acid, with 1000 parts of water. The reaction mixture was agitated under reflux for 3 hours at 66 to 14 0., preferably while maintaining an inert nitrogen atmosphere and shielding the reagents from actiniciight. 'Attthe end oh the aforesaid period,

Lthe'reactionkniixturewas sseparated as in the preceding example, and the organic liquid layer .distilled, whereby 623 parts of methyl a-ChlOIO- acrylate and 239 parts of unreacted methyl afi- These results correspond to a 62% conversion of the met'hyl -a, 3-dichloropropionate, and a yield of :methyl a-chloroacrylate corresponding to 76% oftheory.

Example 3 457 parts (1 mol) of methyl a,fi-di0h1010- propionate containing 1.7 parts of tertiary butyl catechol as a polymerization inhibitor were added to a solution obtained by neutralizing 140 "parts by volume of 85% phosphoric acid ='(-2'.05

mols) with 160 parts ("4 mols) of sodium :hydroxide in 500 parts-of water. The-pH o'f-the resulting aqueous solution was 6. 'The' mixture was agitated and heated to boiling temperature under reflux while protected from light and air as in the preceding examples. At--'the* end- 61 this period, the pH of 'the'a'queous solution in the reaction mixture was between "4 and 5. The mixture was "separated into'aqueous organic layers, and the latter 'dlst'illed'as inthe preceding examples. 91 parts or "methyl 4:- chloroacrylate and 1-8 'parts 'of methyl 'ap-di- 'chl'oropropionate were thus recovered, *coiresponding to a conversion of "75% and a F-yield of methyl a-chloroacrylate oresor theory.

Example 4 1 57 parts (1 mol) of methyl a;',B-dichloropropionate containing 117 parts of tertiary-bowl catechol as a polymerization inhibitor, "were mixed with a solution-obtained-by ne1itralizing 210 parts by volume of 85% phosphoric a'oid (3.08 mols) with 240 parts 6 =mo'1slof sodium hydroxide in 500 parts of water. The pHof the aqueous solutionwas 6. The reaction mixture, protected from light and --air #as in *the preceding examples, washea'ted at polling temperature under reflux and agitated "for 1% hours. At the end of this period/the pH- rem'ained about 6. The "mixture was then woi ked up as described in the preceding examples, yielding 64 parts of methyl a-chloroaciylate and 37' parts of methyl a,-p-dichloropropionate, corresponding to 53% conversion -and 10% *of theoretical yield-of methyl -q-'chloroacrylate.

The phosphates employed for -"'dehydrclh'alio genation in accordance withthis invention are the alkali metal (sodium or-potassium) monohydrogen phosphates, including aik'al'i -meta l ammonium monohydrogen phosphates.

The concentration and proportions of these. salts in the reaction mixture, -'and-*-thetemperatures disclosed in the 'examples can be'va'ried within the ranges discussed above to obtain similar dehydrohalogenationresults. "Ihe'a'queous solution "containing the aforesaid alkaii metal monohydrogen phosphate 'has a pH 6f 4 to :8, and preferably between '4wand 7-, tmoughout practically-all of'thereabtion. by reason b! the formation 'or presence therein of alkali metal dihydrogen phosphates. The preferred pH range during the reaction is 5 to 6. (The pH values and ranges referred to herein are those determinant-25 C.)

The esters to which the process illustrated above can be applied are the esters of a,aand a,,B-diChlOl'0-, dibromoand -diiodopropionic acids, but the process is most conveniently applied to esters of a,s-dichloropropionic acid. Such esters include the alkyl esters, e. g. methyl, ethyl, isopropyl, butyl, amyl, isoamyl, n-hexyl, octyl, lauryl and oct-adecyl esters of the aforesaid acids. In addition, there may he mentioned the corresponding alkenyl esters, such as allyl, methallyl, crotyl, oleyl and chloroallyl esters. The process can also be applied to polyhydric alcohol esters of the aforesaid acids, e. g. to the glycol, glycerol, sorbitol and mannitol esters, as well as to the aryl, aralkyl, cyclcparaffinic and heterocyclic esters such as, for example, the phenyl, cresyl, resorcyl, naphthyl, benzyl, fenchyl, cyclohexyl and furfuryl esters. All of these esters yield the corresponding a-haloacrylic esters upon dehydrohalogenation by the procedure disclosed above and illustrated in the examples. Moreover, the procedure of this invention is not only applicable to the esters of the aforesaid a,aand a,/3-dihalopropionic acids, but also to the corresponding nitriles, amides and Nmonoand disubstituted amide in which the nitrogen substituents can be aliphatic, araliphatic, cycloaliphatic, aromatic, or heterocyclic, as for example, the monoand dimethylamides, monoand diethylamides, the B-hydroxyethylamides, the cyclohexyland cyclohexylmethylamides, the benzyland benzylmethylamides, the anilides, the morpholides or piperidides of a,B-dichloropropicnic acid. These compounds, like the esters, yield the corresponding a-haloacrylic acid compounds by the same procedure as that employed for the esters of these acids.

Variations and modifications which will be obvious to those skilled in the art can be made in the specific procedures disclosed above without departing from the scope or spirit of the invention.

Iclaim:

1. A process for the preparation of an ester, amide, or nitrile of an a-haloacrylic acid, which comprises dehydrohalogenating a member of the group consisting of the esters, nitriles, amides and N-substituted amides of dichloro-, dibromo-, and diiodo-propionic acids containing at least one of its substituent halogens in aposition, by heating in the presence of an aqueous solution of an alkali metal monchydrogen phosphate, having a pH not exceeding 8.

2. A process for the preparation of an ester, amide, or nitrile of an a-haloacrylic acid, which comprises dehydrohalogenating a member of the group consisting of the esters, nitriles, amides and N-substituted amides of dichloro-, dibromo-, and diiodc-propicnic acids containing at least one of its substituent halogens in aposition, by heating in the presence of an aqueous solution of an alkali metal monohydrogen phosphate, further containing an alkali metal dihydrcgen phosphate, the pH of said solution being between dand 7.

3. A process for the preparation of an ester, amide, or nitrile of an a-haloacrylic acid, which comprises dehydrohalogenating a member of the group consisting of the esters, nitriles, amides and N-substituted amides oi dichlom-. dibromo-,

and diiodc-propionic acids containing at least one of its substituent halogens in aposition, by heating in the presence of an aqueous solution of an alkali metal monchydrogen phosphate, further containing an alkali metal dihydrogen phosphate, the pH of said solution being between 4 and '7, wherein the concentration of said alkali metal monohydrogen phosphate is maintained at at least 10% throughout the reaction.

4. A process for the preparation of an ester, amide, or nitrile of an a-haloacrylic acid, which comprises heating a mixture of 1 mol of a member of the group consisting of the esters, nitriles, amides and N-substituted amides of dich1oro-, dibromo-, and diiodo-propionic acids having at least one of its substituent halogen atom in aposition, with an aqueous solution having a pI-l of 4 to 8 and containing 1 to 3 mols of an alkali metal monohydrogen phosphate in a concentration of at least 10% at a temperature from 60 to C.

5. A process for the preparation of an ester of a-chloroacrylio acid, which comprises heating the corresponding ester of B-dihalopropionic acid at a temperature from 60 to 110 C. with an aqueous solution of an alkali metal monohydrogen phosphate together with an alkali metal dihydrogen phosphate, said solution having a pH between 4 and 7, and the concentration of said alkali metal monohydrogen phosphate being at least 10% throughout the reaction.

6. A process for the preparation of methyl a-chloroacrylate, which comprises heating methyl a,,8-dichloropropionate at a temperature from 60 to 110 C. with an aqueous solution of an alkali metal monohydrogen phosphate together with an alkali metal dihydrogen phosphate, said solution having a pH of 5 to 6, the concentration of said alkali metal monohydrogen phosphate being initially at least 30% and the amount thereof being sufficient to maintain the concentration thereof above 10% throughout the reaction.

7. A process for the preparation of methyl u-chloroacrylate, which comprises adding methyl a,/3-dichloropropionate to a solution in water of disodium hydrogen phosphate amounting to 1 to 3 mols per mol of a,,6-dichloropropionate, the concentration of said phosphate in said solution being at least 30%, and heating the reaction mixture at 60 to 110 C.

8. A process for the preparation of methyl a-chloroacrylate, which comprises adding methyl a,c-dichloropropionate to a solution in water of sodium monohydrogen phosphate together with a minor amount of sodium dihydrogen phosphate in suflicient amount to yield a pH below '7, the concentration of said disodium hydrogen phosphate being initially at least 30%, and the amount thereof at least sumcient to maintain the concentration above 10% throughout the reaction.

WILLIAM O. NEY, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number 

5. A PROCESS FOR THE PREPARATION OF AN ESTER OF A-CHLOROACRYLIC ACID, WHICH COMPRISES HEATING THE CORRESPONDING ESTER OF A,B-DIHALOPROPIONIC ACID AT A TEMPERATURE FROM 60 TO 110* C. WITH AN AQUEOUS SOLTUION OF AN ALKALI METAL MONOHYDROGEN PHOSPHATE TOGETHER WITH AN ALKALI METAL DIHYDROGEN PHOSPHATE, SAID SOLUTION HAVING A PH BETWEEN 4 AND 7, AND THE CONCENTRATION OF SAID ALKALI METAL MONOHYDROGEN PHOSPHATE BEING AT LEAST 10% THROUGHOUT THE REACTION. 